In the prior art, there is a known living body information measuring apparatus which, for measurement, compresses a part such as wrist, upper arm, finger or ankle by using a fluid bag supplied with a fluid such as air. A known blood pressure monitor uses the oscillometric method to measure the blood pressure. In the oscillometric method, a fluid bag is first wrapped around a tissue of a living body, and fixed. Then, either while a pressure is applied to the tissue of the living body by feeding the fluid into the fluid bag until the arteries of the tissue of the living body are completely occluded, and thereafter the pressure of the fluid bag is gradually reduced at a constant rate, or while the pressure of the fluid bag is increased by feeding the fluid thereinto at a constant rate until the arteries of the tissue of the living body are completely occluded, the method uses a sensor to detect a pulse wave signal of the arteries superimposed on the pressure of the fluid bag, and measures systolic and diastolic blood pressures thereof based on the amplitude variation of this signal by using a predetermined algorithm. Thus, this method needs to compress the arteries at a predetermined pressure so as to accurately detect a change in the arteries
Now, multiple arteries are present in a living body part such as wrist, finger and ankle. For example, two arteries, radial artery and ulnar artery, are present on the palm side of the wrist, and three arteries are present in the ankle, while two arteries and one artery are present on the palm side and on the dorsal side of a finger, respectively. Further, various bones, muscles and tendons are present near these arteries and are involved in the movement of the living body parts. For example, a long palmar muscle, a flexor carpi radialis tendon, a flexor carpi ulnaris tendon, a flexor digitorum superficialis tendon and a flexor digitorum profundus tendon are present on the palm side of the wrist. Wrist bending is produced by the contraction of the long palmar muscle and the flexor carpi radialis tendon. On the other hand, finger bending is produced by the contraction of the flexor digitorum superficialis tendon and the flexor digitorum profundus tendon. Thus, the living body parts have complex structures.
When a wrist or a finger is bent as described above, tendons present on the surface of the wrist bulge, and the tendons become tense and tight. Therefore, if the above-described method is used to measure blood pressure, the bulged tendons may, in some cases, hinder the compression on the arteries as applied by the fluid bag, and there is a possibility that contact intimacy between the fluid bag and the living body part may become poor. Thus, there may be a case where the arteries cannot be occluded unless the pressure of the fluid bag is set higher than a predetermined pressure, leading to a problem that a reduction in the detectability of a pulse wave signal of the arteries is likely to cause measurement errors.
Thus, as described e.g. in Japanese Patent (sic, correctly: Japanese Patent Publication) 2003-290156, a blood pressure monitor is proposed in which a cuff to compress the arteries is formed by a plurality of fluid bags corresponding in number and positions to the respective arteries, and in which these fluid bags are connected to each other, each having a stacked structure in the direction of compressing the artery. FIG. 14 shows a cross-sectional view in a state where the cuff of the blood pressure monitor compresses a wrist. Note that only a wrist 5 and a cuff 2 are shown for convenience, omitting the showing of a main body of the blood pressure monitor and others.
The wrist 5 is composed e.g. of a radial artery 10, an ulnar artery 11, and tendons 14 which are related to the movements of the wrist 5 and fingers. The cuff 2 has fluid bags 101, 102 divided left and right with the tendons 14 therebetween, in which the fluid bag 101 and the fluid bag 102 respectively compress the radial artery 10 and the ulnar artery 11. The cuff 2 having such a structure can measure accurate living body information because the respective fluid bags 101, 102 compress the radial artery 10 and the ulnar artery 11.
However, the compression force of the fluid bags 101, 102 to the tendons 14 is weak, so that the bulge of the tendons 14 due to e.g. the bending of the wrist 5 may not be suppressed in some cases. Therefore, if the tendons 14 bulge, the contact intimacy between the cuff 2 and the wrist 5 becomes poor, so that the compression force to the radial artery 10 and the ulnar artery 11 becomes weak. Thus, there may be a case where the radial artery 10 and the ulnar artery 11 cannot be occluded, unless the pressure of the fluid bags 101, 102 is set higher than a predetermined pressure. As a result, this may cause measurement errors in some cases.
Further, if a user attaches the blood pressure monitor at a position shifted around the wrist 5 from a predetermined position, the contact intimacy of the fluid bags 101, 102 with the radial artery 10 and the ulnar artery 11 becomes weak. This weakens the compression force to the radial artery 10 and the ulnar artery 11, which may cause measurement errors in some cases. In order to prevent this, a method is known in which a hard clip board or the like is provided inside the cuff 2. However, this has a problem that it is difficult for the user to attach it. Further, if the wrist or the fingers are bent inward or bent outward, the intimate contact state of the fluid bags 101, 102 with the radial artery 10 and the ulnar artery 11 changes, thereby causing a change in the compression state. Thus, it is required to provide a control jig for controlling the postures of the wrist and fingers, reducing the portability of such blood pressure monitor. In addition, in order to prevent the user from bending the wrist or fingers inward, it is required to limit its posture for measurement, which may, in some cases, force the user to perform measurements in an unnatural posture.
Further, as described in Japanese Patent (sic, correctly: Japanese Patent Publication) 2003-24286, a blood pressure monitor is proposed in which a cuff is formed of a fluid bag which is not divided left and right. FIG. 15 shows a cross-sectional view in a state where the cuff of the blood pressure monitor compresses a wrist. Note that only a wrist 5 and a cuff 2 are shown for convenience, omitting the showing of a main body of the blood pressure monitor and others. The cuff 2 has a substantially circular-shaped fluid bag 103 to cover the wrist 5. The fluid bag 103 compresses the wrist 5 regardless of the presence of tendons 14.
The fluid bag 103 has a substantially circular-shaped cross section, so that it generally has a property that its central portion expands most while an expansion of its side portions is small. Thus, the compression force of the fluid bag 103 to the tendons 14 is strong to be able to suppress the bulge of the tendons 14 due to the bending of the wrist or fingers. However, the contact intimacy of the fluid bag 103 with the radial artery 10 and the ulnar artery 11 is weak, causing the compression force to be weak, which may cause measurement errors in some cases.